Tag: hydrogen ion scale or the ph scale

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Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

$\displaystyle \underset {orange}{Cr _2O _7^{2-}}\,\overset {pH=x}{ \underset {pH = y}{\leftrightarrows}}\, \underset {green}{CrO _4^{2-}}$. 


This change is based on change in pH. 

Find values of x and y  :

  1. $8, 6$
  2. $8, 10$
  3. $4, 6$

  4. change is independent of pH
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The process involves the equilibrium between chromate (VI), dichromate (VI) and hydrogen ions:


$2{ Cr{ O } _{ 4 }^{ 2- } } _{ \left( aq. \right)  \left( yellow \right)  }+2{ { H }^{ + } } _{ \left( aq. \right)  }\rightleftharpoons { { Cr } _{ 2 }{ O } _{ 7 }^{ 2- } } _{ \left( aq. \right)  \left( orange \right)  }+{ { H } _{ 2 }O } _{ \left( l \right)  }$

The addition of acid encourages the equilibrium towards the right (pH=6), producing more orange colored dichromate (VI) ions. The addition of hydroxide ions causes the concentration of hydrogen ions to decrease, and this brings the equilibrium back to the left-hand side, regenerating yellow chromate (VI) ions.

Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry
Unknown metal Appearance Reactions with dilute HCl Reaction with dilute HNO$ _3$
  (1) Dull gray solid with white oxide coating  Dissolved with bubbles of clear gas  Dissolved with bubbles of clear gas
  (2) Solid; lustrous smooth silver-gray surface No reaction  Dissolved with bubbles of orange gas

Which of the following represents unknown metal (2) ?

  1. Carbon

  2. Copper

  3. Zinc

  4. Sodium

  5. Silver
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Unknown metal (2) could be silver. It is a relatively inert metal. 
Note: Carbon is not a metal. Copper is brownish, zinc is reactive metal with whitish oxide coat in air. Sodium is highly reactive and explodes when it comes in contact with water. It reacts with acids even violently.

Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry
Unknown metal Appearance Reactions with dilute HCl Reaction with dilute HNO$ _3$
  (1) Dull gray solid with white oxide coating  Dissolved with bubbles of clear gas  Dissolved with bubbles of clear gas
  (2) Solid; lustrous smooth silver-gray surface No reaction  Dissolved with bubbles of orange gas

The transparent gas is produced by the addition of dilute HCI to unknown metal (1). Which of the following represents the transparent gas ?  

  1. Cl$ _2$
  2. H$ _2$
  3. O$ _2$
  4. CO$ _2$
  5. NO$ _2$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When dilute $HCl$ is added to the unknown metal  (1) (zinc), the transparent gas produced is hydrogen. 
Note: Chlorine and $NO _2$ gases are green and orange coloured respectively. $CO _2$ is not possible as no $C$ atoms are present.
Also, metals react with acids to form hydrogen gas.

Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

What can be used to measure the strength of acidity or basicity of a solution?

  1. Litmus paper

  2. pH meter
  3. Both $A$ and $B$

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The pH meter is a device used for measuring ph, which is either the concentration or the activity of hydrogen ions in an aqueous solution. It usually has a glass electrode plus a calomel reference electrode or a combination of an electrode.

Multiple choice hydrogen ion scale or the ph scale inorganic analysis chemical analysis and investigation practical work chemistry

What is pH?

  1. Used in identification of cations

  2. Identification of non metals

  3. Specify the acidity or basicity of an aqueous solution
  4. Both $A$ and $C$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$pH$ is a numeric scale used to specify the acidity or basicity of an aqueous solution. It is roughly the negative of the logarithm to base 10 of the concentration, measured in units of moles per liter, of hydrogen ions or $H^+$.